Analog inputs: How to wire analog inputs


ACE are available with some number of general analog inputs.

ACE analog input interfaces are available for either 0-5 VDC, 0-10 VDC or 0-20 mA.

Analog inputs are normally used to connect to sensors outputs. Such sensors measure some physical parameter, such as pressure, temperature, liquid level, position, pH level or other such continuously variable measurement.

The sensors signal output should be connected to a signal input on the analog port and the sensors return or ground reference line must be connected to the PLC ground, next to signal 1 (or otherwise connected to the PLC’s ground).

ACE with current analog input ports (part number ending in ‘c’) should be used for analog current signals between 0 and 20 mA. The two most common type of current signals are 4-20 mA and 0-20 mA. Full range analog signals will convert to a value between 0 and 4095 (12 bits). For 4-20mA inputs, the converted value will be between 820 and 4095. The Scale function in vBuilder can be used to automatically convert the signal value to meaningful data.

For ACE that have a full 8 position port dedicated to analog inputs, the pin next to the sixth input is connected to the PLC’s internal 5V, through a 10 ohm resistor and a diode. This is provided to power a future analog input simulator. It servers no other purpose and should remain unconnected for application use. Analog input ports that do not occupy the full 8 position port do not have this connection.

The 0-20mA analog inputs have a 100 ohm resistor between the input and ground.  For the 0-10V inputs, its 1Mohm.  For the 0-5V inputs, its 499 Kohms.

About 0-20 mA analog inputs

Internally, we convert the 0-20/4-20mA signal to a 0-2V signal by use of a 100 ohm resistor to ground.
That means that the transistor ground and the transducer ground must be the same ground.
If you want to connect the same signal to multiple devices, it won’t work, unless the PLC is the last device in the chain and every other devices can handle the pass through.

How to convert current 4-20 mA output from a sensor to 0-10 V voltage using resistor ?

See this page

How to change the current of the 0-20 mA input using a simple potentiometer?

You can use a 1 kOhm resistor (R1) and a 1 kOhm potentiometer (R2).
Internally in the ACE, the current is converted to voltage (VM1 = 0-2 V) via a 100 oHm resistor (Rin).


See also More details about the analog input signal of ACE PLCs